Conventionally, a thermal transfer type printing device has been widely utilized in which an ink ribbon is heated by a thermal head and ink applied on the ink ribbon is transferred to and printed on a printing medium. In the printing device, ink having a shape which is the same as an image printed on the printing medium is printed from the ink ribbon and thus, after the printing is performed, a printed trace of ink having the same shape as the printed image is left on the ink ribbon. Therefore, when the printed trace is observed or, when the portion of the ink ribbon where ink has not been printed is thermally transferred again, the image printed on the printing medium can be recognized easily.
In recent years, a card issuing system including a thermal transfer type printing device in which, when a card is conveyed through a card conveying passage, character information or the like is printed on a surface of a card by a thermal head, a hot stamp or the like has been increasingly installed in a store of a financial institution such as a bank. In the printing device for the card issuing system, there may occur a problem that an administrator of the device can easily obtain the image printed on the card from a printed trace of ink which is left in the used ink ribbon, or that a third person can easily obtain the image printed on the card from a printed trace of ink which is left in the used ink ribbon having been discarded. This is an issue to be solved in these days when protection of personal information is regarded very important.
Conventionally, a thermal transfer type printing device has been proposed which is capable of solving the above-mentioned problem (see, for example, Patent Literature 1). In the printing device described in Patent Literature 1, an image which is to be printed on a printing paper is divided into plural portions in a conveyance direction of the printing paper and, when respective portions of the divided images are to be printed, portions to be used of the ink ribbon are randomly changed by using a fast forwarding operation and a rewinding operation of the ink ribbon. Therefore, in the printing device, unless printed traces of ink which are left on the ink ribbon having been used are analyzed in detail, the image printed on the printing paper cannot be obtained and, as a result, personal information printed on the printing paper is protected.